In the framework of the CROSTVOC (CROp STress VOC) project, the exchange of biogenic volatile organic compounds (BVOCs) between two important agricultural crop species, maize and winter wheat, and the ... [more ▼]

In the framework of the CROSTVOC (CROp STress VOC) project, the exchange of biogenic volatile organic compounds (BVOCs) between two important agricultural crop species, maize and winter wheat, and the atmosphere has recently been measured during an entire growing season by using the eddy covariance technique. Because of the co-variation of BVOC emission drivers in field conditions, laboratory studies were initiated in an environmental chamber in order to disentangle the responses of the emissions to variations of the individual environmental parameters (such as PPFD and temperature) and to diverse abiotic stress factors. Young plants were enclosed in transparent all-Teflon dynamic enclosures (cuvettes) through which BVOC-free and RH-controlled air was sent. BVOC enriched air was subsequently sampled from the plant cuvettes and an empty cuvette (background) and analyzed for BVOCs in a high sensitivity Proton-Transfer Reaction Mass Spectrometer (hs-PTR-MS) and for CO2 in a LI-7000 non-dispersive IR gas analyzer. Emissions were monitored at constant temperature (25 °C) and at a stepwise varying PPFD pattern (0-650 µmol m-2 s-1). For maize plants, sudden light/dark transitions at the end of the photoperiod were accompanied by prompt and considerable increases in methanol (m/z 33) and water vapor (m/z 39) emissions. Moreover, guttation droplets appeared on the sides and the tips of the leaves within a few minutes after light/dark transition. Therefore the assumption has been raised that methanol is also coming out with guttation fluid from the leaves. Consequently, guttation fluid was collected from young maize and wheat plants, injected in an empty enclosure and sampled by PTR-MS. Methanol and a large number of other compounds were observed from guttation fluid. Recent studies have shown that guttation from agricultural crops frequently occurs in field conditions. Further research is required to find out the source strength of methanol emissions by this guttation phenomenon in real environmental conditions. [less ▲]

archiDART is an R package allowing the analysis of complex plant root system architectures using the output files created by Data Analysis of Root Tracings (DART), an open-access software dedicated to the ... [more ▼]

archiDART is an R package allowing the analysis of complex plant root system architectures using the output files created by Data Analysis of Root Tracings (DART), an open-access software dedicated to the study of plant root architecture and development across time series (Le Bot et al (2010) DART: a software to analyse root system architecture and development from captured images, Plant and Soil, 326, 261--273). [less ▲]

The allelopathic activity of barley (Hordeum vulgare L. ssp. vulgare) root exudates was studied by comparing their effects on seedling establishment in barley itself and in two weed species, Bromus ... [more ▼]

The allelopathic activity of barley (Hordeum vulgare L. ssp. vulgare) root exudates was studied by comparing their effects on seedling establishment in barley itself and in two weed species, Bromus diandrus Roth. and Lolium rigidum Gaudin, using an original laboratory protocol, named ‘seed-after-seed’. In this protocol, the donor and the receiver species of watersoluble allelochemicals are grown one after the other in the same dishes, in conditions reducing resource competition between both species. Growth of all receptive species (weeds and barley) was inhibited in a dose-dependent manner, when using increasing barley seed densities (0, 8, 19 and 25 seeds per Petri dish). In our conditions, the barley varieties and landraces exhibited different allelopathic activities against weeds or barley. The allelopathic potential of the barley root exudates was also dependent on the receiver species. Indeed, the released allelochemicals proved to be more toxic against the weed plants than on barley itself. Furthermore, the toxicity of the allelochemicals increased after their release by roots, between day 0 and day 6. These allelochemicals might contribute to the plant community dynamics and their usefulness as bio-herbicides deserves further consideration. [less ▲]

In chemical ecology, the roles played by root-emitted volatile organic compounds (VOCs) in biotic interactions and the quantitative analysis of such chemicals in root tissues remain poorly documented. In ... [more ▼]

In chemical ecology, the roles played by root-emitted volatile organic compounds (VOCs) in biotic interactions and the quantitative analysis of such chemicals in root tissues remain poorly documented. In this context, this study aims at using a fully automated gas chromatography – mass spectrometry methodology allowing both identification and accurate quantification of VOCs produced by roots of a monocotyledonous plant species at five selected developmental stages from germination to the end of tillering. Results show that barley roots mainly produce four volatile aldehydes, namely hexanal, (E)-hex-2-enal, (E)-non-2-enal and (E,Z)-nona-2,6-dienal. These molecules are well-known linoleic and linolenic acid derivatives produced via the lipoxygenase/hydroperoxide lyase pathway of higher plants. Our findings contrast with analyses documented on aboveground barley tissues that mainly emit C6 aldehydes, alcohols and their corresponding esters. Multivariate statistical analyses performed on individual VOC concentrations indicate quantitative changes in the volatile profile produced by barley roots according to plant age. Barley roots produced higher total and individual VOC concentrations when young seminal roots emerged from the coleorhizae compared to older phenological stages. Moreover, results also show that the C6/C9 volatile aldehyde ratio was the lowest at the end of tillering while the maximum mean value of this ratio was reached in seven day-old barley roots. [less ▲]

Water stress is one of the major environmental factors limiting the crop productivity . Plant stress responses are very complex and drought tolerance may be linked to the presence of specific ... [more ▼]

Water stress is one of the major environmental factors limiting the crop productivity . Plant stress responses are very complex and drought tolerance may be linked to the presence of specific microorganisms in the rhizosphere. Indeed, some plant growth promoting bacteria (PGPR) strains have been found to improve plant growth under abiotic stresses. Among the many mechanisms by which those PGPR can support plant growth, the emission of volatile organic compounds (VOCs) and their biological impact are still under study. The aim of this work is to evaluate the interaction between the model grass Brachypodium distachyon (Bd21) and two strains of PGPR. The impact of volatile emission on Bd21 growth was studied using an ex-vitro cocultivation system without physical contact between plant and bacteria during 10 days. This peculiar system was developed to assess bacterial VOCs impacts on plants under realistic growth and stress conditions. In parallel, the response of Bd21 seedlings to water deficit induced by polyethylene glycol 6000 (PEG 6000) was studied to establish contrasted growth conditions regarding water availability [less ▲]

Abiotic and biotic stresses are known to alter biogenic volatile organic compound (BVOC) emission from plants. With the climate and global change, BVOC emissions are likely to increase. This increase on ... [more ▼]

Abiotic and biotic stresses are known to alter biogenic volatile organic compound (BVOC) emission from plants. With the climate and global change, BVOC emissions are likely to increase. This increase on BVOC emissions could be driven by many environmental parameters like temperature, ozone and light availability for photosynthesis although it is still difficult to predict the impact of some environmental parameters, environmental controls on BVOC emission being species and BVOC-dependent. These BVOC are involved in a wide range of interactions of plants with their environment and these interactions could be affected by the global change. Moreover, BVOC also play a key role in the atmospheric chemistry and may contribute to ozone formation and an increase in methane lifetime, strengthening the global change. Yet, due to technical limitation, there are few studies examining the impact of multiple co-occurring stresses on BVOC emission at the ecosystem level although stress combination is probably more ecologically realistic in field. In the CROSTVOC (for CROp STress VOC) project, the impact of abiotic stresses (e.g. heat, drought, ozone and grazing) on BVOC emission will be investigated for field crops (maize and wheat) and grassland both at the ecosystem and plant scale. [less ▲]

In agriculture, phosphorus (P) is considered as the second most growth-limiting macronutrient after nitrogen. However, P fertilizers are produced from non-renewable resources. In this context, sustainable ... [more ▼]

In agriculture, phosphorus (P) is considered as the second most growth-limiting macronutrient after nitrogen. However, P fertilizers are produced from non-renewable resources. In this context, sustainable production strategies have to be developed to enhance P use efficiency of crops, e.g. based on naturally occurring biotic interactions that limit the negative impacts of P deficiency in soils. Plant growth-promoting rhizobacteria (PGPR) have already revealed their ability to promote plant growth and tolerance to abiotic stresses through many mechanisms. Among them, the bacterial volatile organic compounds-mediated communication between plants and PGPR is still poorly documented. Our research project aims at studying the capacity of a model cereal plant (Brachypodium distachyon (L.) Beauv. Bd21) to face P deficiency in interaction with PGPR. The prerequisite of this project consists in characterizing Bd21 response to P deficiency by measuring plant biomass production and allocation, root system architecture, total phosphorus content, root-secreted and intracellular acid phosphatase activity under various P concentrations. Those results will allow us to define P-limiting conditions, in order to assess PGPR volatiles influence on plant response to P deficiency. This approach will use an ex-vitro co-cultivation system allowing volatiles-mediated interaction and should help us to unravel the ability of rhizobacterial volatiles to enhance plant tolerance to P deficiency. [less ▲]

In chemical ecology, the roles played by root-emitted volatile organic compounds (VOCs) in biotic interactions and the quantitative analysis of such chemicals in root tissues remain poorly documented. In ... [more ▼]

In chemical ecology, the roles played by root-emitted volatile organic compounds (VOCs) in biotic interactions and the quantitative analysis of such chemicals in root tissues remain poorly documented. In this context, this study aims at developing a fully automated analytical methodology allowing both identification and accurate quantification of VOCs produced by roots of a monocotyledon plant species. Briefly, VOC emitted by crushed barley roots are successively trapped by dynamic headspace sampling on Tenax TA adsorbents, thermally desorbed and cryofocused, separated by gas chromatography (GC) and finally analysed by mass spectrometry (MS) in both SCAN and selected ion monitoring modes. Results show that barley roots mainly produce four volatile aldehydes, namely hexanal, (E)-hex-2-enal, (E)-non-2-enal and (E,Z)-nona-2,6-dienal. These molecules are well-known linoleic (C18:2) and linolenic (C18:3) acid derivatives produced via the lipoxygenase and the hydroperoxide lyase pathways of higher plants. Our findings contrast with analyses documented on aboveground barley tissues that mainly emit C6 aldehydes, alcohols and their derivative esters. Moreover, preliminary results indicate quantitative changes in the volatile profile contained in barley roots according to plant age. Multivariate statistical analyses are currently underway to quantitatively assess these changes using plants at five selected developmental stages ranging from germination to the end of tillering. [less ▲]

In 2010, Le Bot et al presented a free and open-access software (Data Analysis of Root Tracings - DART) allowing the analysis of complex root system architectures from captured images, particularly across time series. Using this software, a user has to manually identify roots as a set of links. After vectorization of a root system, three final data sets (RAC, TPS and LIE) can be exported as table files containing several attributes for (a) each individual root (e.g. root length), (b) each observation day or (c) each point used to construct the vectorized root system respectively. These data sets can finally be used either to calculate derived root system architecture (RSA) parameters or to draw the root system architecture at selected observation dates. However when an experiment involves the analysis and comparison of many root systems, the calculation of RSA parameters for each data set and the drawing of the corresponding vectorized root systems become time-consuming. In this context, we developed a R package, called archiDART, allowing both the automatic calculation of common root architecture parameters and the X-Y plotting of vectorized root systems for selected observation dates. [less ▲]

Control methods commonly used to suppress the great brome (Bromus diandrus Roth., syn. Bromus rigidus Roth. subsp. gussonii Parl.) in Tunisian cereal crop are essentially chemical, raising both efficacy and safety issues. The introduction of allelopathic species into the crop rotation or utilizing allelopathic plants as living/green mulches has been suggested as a cost-effective way to reduce the weed presence. Among these species, the sunflower (Helianthus annuus L.) has shown an allelopathic potential against some troublesome weed species. In this study, we analyzed the biological activities of water extract of different tissues (root, shoot, leaf and flower) of sunflower on the seedling establishment of the great brome. In a second experiment, the allelopathic influence of sunflower residues (leaf or flower) against this weed was also studied under glasshouse conditions at more advanced stages of growth using different concentrations (0, 6, 12 and 18g tissue dry weight / kg of soil). The first experiment showed an effect depending on the parts of the sunflower. Indeed, the roots seem to be the less allelopathic part (22% of root inhibition growth) as compared to the leaves and flowers (82% and 100%, respectively). This potential seems to simultaneously affect the radicle and the coleoptile growth of the great brome. In the second experiment, weed growth was inhibited in a dose-dependent manner, using increasing amounts of sunflower residues. The allelopathic potential of the leaves or flowers reduced both the root or shoot length and biomass accumulation of the weed. These results suggest that the sunflower can be a good previous crop for cereal cultivation by controlling the presence of some weeds, including the great brome. In this perspective, the inhibitory effects of sunflower residues on cultivated cereals in the field need to be assessed. [less ▲]

Cellular totipotency is one of the basic principles of plant biotechnology. Currently, the success of the procedure used to produce transgenic plants is directly proportional to the successful insertion ... [more ▼]

Cellular totipotency is one of the basic principles of plant biotechnology. Currently, the success of the procedure used to produce transgenic plants is directly proportional to the successful insertion of foreign DNA into the genome of suitable target tissue/cells that are able to regenerate plants. The mature embryo (ME) is increasingly recognized as a valuable explant for developing regenerable cell lines in wheat biotechnology. We have previously developed a regeneration procedure based on fragmented ME in vitro culture. Before we can use this regeneration system as a model for molecular studies of the morphogenic pathway induced in vitro and investigate the functional links between regenerative capacity and transformation receptiveness, some questions need to be answered. Plant regeneration from cultured tissues is genetically controlled. Factors such as age/degree of differentiation and physiological conditions affect the response of explants to culture conditions. Plant regeneration in culture can be achieved through embryogenesis or organogenesis. In this paper, the suitability of ME tissues for tissue culture and the chronological series of morphological data observed at the macroscopic level are documented. Genetic variability at each step of the regeneration process was evaluated through a varietal comparison of several elite wheat cultivars. A detailed histological analysis of the chronological sequence of morphological events during ontogeny was conducted. Compared with cultures of immature zygotic embryos, we found that the embryogenic pathway occurs slightly earlier and is of a different origin in our model. Cytological, physiological, and some biochemical aspects of somatic embryo formation in wheat ME culture are discussed. [less ▲]

Genetically modified organisms (GMOs) and derived food and feed products are subject to a risk analysis and regulatory approval before they can enter the market in the European Union (EU). In this risk ... [more ▼]

Genetically modified organisms (GMOs) and derived food and feed products are subject to a risk analysis and regulatory approval before they can enter the market in the European Union (EU). In this risk analysis process, the role of the European Food Safety Authority (EFSA), which was created in 2002 in response to multiple food crises, is to independently assess and provide scientific advice to risk managers on any possible risks that the use of GMOs may pose to human and animal health and the environment. EFSA's scientific advice is elaborated by its GMO Panel with the scientific support of several working groups and EFSA's GMO Unit. This review presents EFSA's scientific activities and highlights its achievements on the risk assessment of GMOs for the first 10 years of its existence. Since 2002, EFSA has issued 69 scientific opinions on genetically modified (GM) plant market registration applications, of which 62 for import and processing for food and feed uses, six for cultivation and one for the use of pollen (as or in food), and 19 scientific opinions on applications for marketing products made with GM microorganisms. Several guidelines for the risk assessment of GM plants, GM microorganisms and GM animals, as well as on specific issues such as post-market environmental monitoring (PMEM) were elaborated. EFSA also provided scientific advice upon request of the European Commission on safeguard clause and emergency measures invoked by EU Member States, annual PMEM reports, the potential risks of new biotechnology-based plant breeding techniques, evaluations of previously assessed GMOs in the light of new scientific publications, and the use of antibiotic resistance marker genes in GM plants. Future challenges relevant to the risk assessment of GMOs are discussed. EFSA's risk assessments of GMO applications ensure that data are analysed and presented in a way that facilitates scientifically sound decisions that protect human and animal health and the environment. [less ▲]

The rhizobacterium Pseudomonas putida BTP1 stimulates induced systemic resistance (ISR) in tomato. A previous work showed that the resistance is associated in leaves with the induction of the first enzyme ... [more ▼]

The rhizobacterium Pseudomonas putida BTP1 stimulates induced systemic resistance (ISR) in tomato. A previous work showed that the resistance is associated in leaves with the induction of the first enzyme of the oxylipin pathway, the lipoxygenase (LOX), leading to a faster accumulation of its product, the free 13-hydroperoxy octadecatrienoic acid (13-HPOT), 2 days after Botrytis cinerea inoculation. In the present study, we further investigated the stimulation of the oxylipin pathway: metabolites and enzymes of the pathway were analyzed to understand the fate of the 13-HPOT in ISR. Actually the stimulation began upstream the LOX: free linolenic acid accumulated faster in P. putida BTP1-treated plants than in control. Downstream, the LOX products 13-fatty acid hydroperoxides esterified to galactolipids and phospholipids were more abundant in bacterized plants than in control before infection. These metabolites could constitute a pool that will be used after pathogen attack to produce free fungitoxic metabolites through the action of phospholipase A2, which is enhanced in bacterized plants upon infection. Enzymatic branches which can use as substrate the fatty acid hydroperoxides were differentially regulated in bacterized plants in comparison to control plants, so as to lead to the accumulation of the most fungitoxic compounds against B. cinerea. Our study, which is the first to demonstrate the accumulation of an esterified defense metabolite during rhizobacteria-mediated induced systemic resistance, showed that the oxylipin pathway is differentially regulated. It suggests that this allows the plant to prepare to a future infection, and to respond faster and in a more effective way to B. cinerea invasion. [less ▲]